Lubricating oil compositions for internal combustion engines generally contain a variety of additives to reduce or control deposits, wear, corrosion, etc. The present invention is concerned with compositions useful as dispersants in lubricating oil compositions.
In lubricating oils, dispersants function to control sludge, carbon, and varnish produced primarily by the incomplete combustion of the fuel, or impurities in the fuel, or impurities in the base oil used in the lubricating oil composition. Dispersants also control viscosity increase due to the presence of soot in diesel engine lubricating oils.
One of the most effective classes of lubricating oil dispersants is polyalkylene succinimides. In some cases, the succinimides have also been found to provide fluid-modifying properties, or a so-called viscosity index credit, in lubricating oil compositions. That produces a reduction in the amount of viscosity index improver which would be otherwise have to be used.
Polyalkylene succinimides are generally prepared by the reaction of the corresponding polyalkylene succinic anhydride with a polyalkyl polyamine. Polyalkylene succinic anhydrides are generally prepared by a number of well-known processes. For example, there is a well-known thermal process (see, e.g., U.S. Pat. No. 3,361,673), an equally well-known chlorination process (see, e.g., U.S. Pat. No. 3,172,892), a combination of the thermal and chlorination processes (see, e.g., U.S. Pat. No. 3,912,764), and free radical processes (see, e.g., U.S. Pat. Nos. 5,286,799 and 5,319,030). Such compositions include one-to-one monomeric adducts (see, e.g., U.S. Pat. Nos. 3,219,666 and 3,381,022), as well as "multiply adducted" products, adducts having alkenyl-derived substituents adducted with at least 1.3 succinic groups per alkenyl-derived substituent (see, e.g., U.S. Pat. No. 4,234,435).
U.S. Pat. Nos. 3,361,673 and 3,018,250 describe the reaction of an alkenyl- or alkyl-substituted succinic anhydride with a polyamine to form alkenyl or alkyl succinimide lubricating oil dispersants and/or detergent additives.
U.S. Pat. No. 4,612,132 teaches that alkenyl or alkyl succinimides may be modified by reaction with a cyclic or linear carbonate or chloroformate such that one or more of the nitrogens of the polyamine moiety is substituted with a hydrocarbyl oxycarbonyl, a hydroxyhydrocarbyl oxycarbonyl, or a hydroxy poly(oxyalkylene) oxycarbonyl. These modified succinimides are described as exhibiting improved dispersancy and/or detergency in lubricating oils.
U.S. Pat. No. 4,747,965 discloses modified succinimides similar to those disclosed in U.S. Pat. No. 4,612,132, except that the modified succinimides are described as being derived from succinimides having an average of greater than 1.0 succinic groups per long chain alkenyl substituent.
An article by S. T. Roby, R. E. Kornbrekke, and J. A. Supp "Deposit Formulation in Gasoline Engines, Part 2, Dispersant Effects on Sequence VE Deposits" JOURNAL OF THE SOCIETY OF TRIBOLOGISTS AND LUBRICATION ENGINEERS, Vol. 50, 12, 989-995 (December 1994) teaches that the length of the dispersant alkyl side chain influences deposit control performance, and that, at the same nitrogen level, the low molecular weight (side chain 1000 daltons) dispersants that were tested were poorer in controlling deposits than the tested high molecular weight (side chain 2000 daltons) succinimide dispersants. This teaching is also consistent with the prior observation comparing 950 Mn side chain succinimides with 2200 Mn side chain succinimides.
U.S. Pat. No. 4,234,435 teaches a preferred polyalkene-derived substituent group with a Mn in the range of 1500 to 3200. For polybutenes, an especially preferred Mn range is 1700 to 2400.
A variety of post-treatments for improving various properties of alkenyl succinimides are known to the art, a number of which are described in U.S. Pat. No. 5,241,003.
Example 2 of U.S. Pat. No. 5,266,186 discloses the preparation of dispersants by reacting certain polyisobutenyl-succinic anhydride adducts (see footnote 2 of Table 2) with ethylenediamine, followed by reaction with a maleic anhydride/.alpha.-olefin copolymer. The patent teaches that, by functioning as an iron sulfide dispersant, the product is useful to inhibit sludge deposits in refinery processing equipment caused by the heat treatment of hydrocarbon feed stocks.
U.S. Pat. No. 5,112,507 discloses a polymeric ladder type polymeric succinimide dispersant in which each side of the ladder is a long chain alkyl or alkenyl, generally having at least about 30 carbon atoms, preferably at least about 50 carbon atoms. The dispersant is described as having improved hydrolytic stability and shear stress stability, produced by the reaction of certain maleic anhydride-olefin copolymers with certain polyamines. The patent further teaches that the polymer may be post-treated with a variety of post-treatments, and describes procedures for post-treating the polymer with cyclic carbonates, linear mono- or polycarbonates; boron compounds (e.g., boric acid), and fluorophosphoric acid and ammonia salts thereof.
U.S. Pat. Nos. 5,334,321 and 5,356,552 disclose certain cyclic carbonate post-treated alkenyl or alkylsuccinimides having improved fluorocarbon elastomer compatibility, which are preferably prepared by the reaction of the corresponding substituted succinic anhydride with a polyamine having at least four nitrogen atoms per mole. Both of these patents disclose the possibility of borating certain cyclic carbonate post-treated alkenyl or alkylsuccinimides.
U.S. Pat. No. 5,334,321 discloses that higher molecular weight alkenyl or alkylsuccinimides give better detergency than the corresponding lower molecular weight alkenyl or alkylsuccinimides.
Mixtures of borated and carbonated polyalkylene succinimides have been derived from the same molecular weight polyalkylenes. The mixtures show inferior soot dispersancy to the individual borated and carbonated polyalkylene succinimides used alone.
U.S. Pat. No. 5,716,912 discloses polyalkylene succinimides prepared by reacting, under reactive conditions, a mixture of a polybutene succinic acid derivative, an unsaturated acidic reagent copolymer of an unsaturated acidic reagent and an olefin, and a polyamine, then treating those succinimides with cyclic carbonates, linear mono- or polycarbonates or a boron compound.